<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <link rel="stylesheet" href="./styles/index.css" />
    <title>Document</title>
  </head>
  <body>
    <div id="app" class="score-case">
      <div class="table">
        <table>
          <thead>
            <tr>
              <th>编号</th>
              <th>科目</th>
              <th>成绩</th>
              <th>操作</th>
            </tr>
          </thead>
          <tbody v-if="list.length > 0">
            <tr v-for="(item, index) in list" :key="item.id">
              <td>{{ index + 1 }}</td>
              <td>{{ item.subject }}</td>
              <td :class="{red: item.score < 60}">{{ item.score }}</td>
              <td><a href="#" @click.prevent="remove(item.id)">删除</a></td>
            </tr>
          </tbody>
          <tbody v-else>
            <tr>
              <td colspan="5">
                <span class="none">暂无数据</span>
              </td>
            </tr>
          </tbody>

          <tfoot>
            <tr>
              <td colspan="5">
                <span>总分：{{ calc4Sum }}</span>
                <span style="margin-left: 50px">平均分: {{ calc4Average }}</span>
              </td>
            </tr>
          </tfoot>
        </table>
      </div>
      <div class="form">
        <div class="form-item">
          <div class="label">科目：</div>
          <div class="input">
            <input type="text" placeholder="请输入科目" v-model.trim="subject"/>
          </div>
        </div>
        <div class="form-item">
          <div class="label">分数：</div>
          <div class="input">
            <input type="text" placeholder="请输入分数" v-model.number="score"/>
          </div>
        </div>
        <div class="form-item">
          <div class="label"></div>
          <div class="input">
            <button class="submit" @click="add()">添加</button>
          </div>
        </div>
      </div>
    </div>
    <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>

    <script>
      const app = new Vue({
        el: '#app',
        data: {
          list: [
            { id: 1, subject: '语文', score: 20 },
            { id: 7, subject: '数学', score: 99 },
            { id: 12, subject: '英语', score: 70 },
          ],
          subject: '',
          score: ''
        },
        methods:{
            remove(id) {
              // filter：创建一个新数组，包含通过测试的所有元素
                this.list = this.list.filter(item => item.id !== id)
            },
            add() {
                if(this.subject === ''){
                    alert("请输入科目")
                    return
                }
                if(this.score === ''){
                    alert("请输入成绩")
                    return
                }
                if(typeof(this.score) !== 'number' || this.score < 0 || this.score > 100){
                    alert("成绩必须是0-100之间的数字")
                    return
                }

                this.list.unshift({
                    id: +new Date(),
                    subject: this.subject,
                    score: this.score
                })
                this.subject = ''
                this.score = ''
            }
        },
        computed:{
            calc4Sum() {
              // reduce：将数组元素通过回调函数累积为单个值
              /**
               * sum：累加器（初始值为 0）
               * item：当前数组元素
               * item.score：获取每个元素的 score 属性
               * 0：初始值
               * */
                let sum = this.list.reduce((sum, item) => sum + item.score, 0)
                return sum
            },
            calc4Average() {
                if(this.list.length > 0){
                    let average = (this.calc4Sum / this.list.length).toFixed(2)
                    return average
                }else{
                    return 0
                }
            }
        }
      })
    </script>
  </body>
</html>
